Water atomization

In water atomization, a number of operation variables are to be considered in order to properly control the process. The variables include geometry parameters, process parameters, and thermophysical properties of metal/alloy and water. Each design and configuration of an atomization unit are unique and thus only some specific operation conditions may be employed. Many of the variables are interrelated. Therefore, there may exist more than one set of optimum variable combinations for a given atomization unit. 

Heating/ Melting Tundish Material Ceramics/Refractory 

Water atomization is intrinsically a high volume, low cost process. Therefore, it is generally more cost-effective compared to other commercial atomization methods. However, powder purity, 

---

Fig. 6. Intake manifold system with a water-atomizing spray nozzle distributing to four individual cylinders. See text.

P/M Tool Steels. In conventionally produced high alloy tool steels (slowly cooled cast ingots), carbide tends to segregate (48). Segregated clusters of carbide persist even after hot working, and cause undesirable effects on tool fabrication and tool performance. P/M tool steels, on the other hand, provide very fine and uniform carbides in the compact, the final bar stock, and the tools. Several tool steel suppHers consoHdate gas-atomized tool steel powder by HIP to intermediate shapes, which are then hot-worked to final mill shapes. Water-atomized tool steel powder is also available (see also T OOL materials). ... 

When hydrogen and oxygen bum to form water, atoms change the manner in which they are combined together. 

A molecular picture of the combustion of butyric acid to give carbon dioxide and water. Atoms are conserved in the reaction. 

Figure 57.4. The making of nitrogen atomized (NA) and water atomized (WA) alloys.

Radical addition to alkenes has been used in cyclizations in aqueous media. Oshima and co-worker studied triethylborane-induced atom-transfer radical cyclization of iodoacetals and iodoacetates in water.121 Radical cyclization of the iodoacetal proceeded smoothly both in aqueous methanol and in water. Atom-transfer radical cyclization of allyl iodoacetate is much more efficient in water than in benzene or hexane. For instance, treatment of allyl iodoacetate with triethylborane in benzene or hexane at room temperature did not yield the desired lactone. In contrast, the compound cyclized much more smoothly in water and yielded the corresponding y-lactone in high yield (Eq. 3.31). 

Figure 1.7. Shapes of solidified droplets (particles) generated in powder production and spray forming processes, (a) Spherical shape gas-atomized gold alloy particles (b) near-spherical and dendritic shapes water-atomized bronze particles (c) irregular and porous (spongiform) shapes water-atomized zinc particles (d) irregular aggregates water-atomized copper particles (Cour. tesy of Atomizing Systems Ltd., UK.)...

Atomization of melts has, in principle, some similarity to the atomization of normal liquids. The atomization processes originally developed for normal liquids, such as swirl jet atomization, two-fluid atomization, centrifugal atomization, effervescent atomization, ultrasonic piezoelectric vibratory atomization, and Hartmann-whistle acoustic atomization, have been deployed, modified, and/or further developed for the atomization of melts. However, water atomization used for melts is not a viable technique for normal liquids. Nevertheless, useful information and insights derived from the atomization of normal liquids, such as the fundamental knowledge of design and performance of atomizers, can be applied to the atomization of melts. 

Numerous atomization techniques have evolved for the production of metal/alloy powders or as a step in spray forming processes. Atomization of melts may be achieved by a variety of means such as aerodynamic, hydrodynamic, mechanical, ultrasonic, electrostatic, electromagnetic, or pressure effect, or a combination of some of these effects. Some of the atomization techniques have been extensively developed and applied to commercial productions, including (a) two-fluid atomization using gas, water, or oil (i.e., gas atomization, water atomization, oil atomization), (b) vacuum atomization, and (c) rotating electrode atomization. Two-fluid atomization... 

Water Atomization -100 Standard deviation 1.7-2.4 Fe, Cu, Cu alloys, Stainless steels. Tool steels, Ni alloys, Precious metals 104-106 400 15-60 Steel iron 0.5-5 Stainless steel Cu alloys High volume, Low cost Powder purity shapeXow EE... 

Steam Atomization Coarse Carbon-, low-alloy-, stainless steels, Co-, Ni-base superallovs 103 — — Between gas and water atomization Irregular particle shape... 

The metal flow rates and capacity in gas atomization are lower than in water atomization. For example, in batch operations, metal flow rates are normally in the range of 1 to 70 kg/min,... 

Table 2.14. Geometry Parameters in Water Atomization of Melts[145l...

In addition to water atomization, oil atomization using various hydrocarbons (oils) is the only other liquid atomization process used in the atomization of liquid metals. Due to the similarity of these two atomization processes, water atomizers can be readily adapted to oil atomization. Some problems inherent in water atomization, such as powder oxidation, can be avoided in oil atomization. The cost-effectiveness is superior to gas atomization, but not as good as water atomization. 

Rotating electrode atomization may be applied to almost all metals and alloys since it does not require a crucible for melting and/ or pouring. In particular, high melting-temperature metals and alloys, such as Ti and Zr, are well suited for the process. However, the production cost is still a drawback associated with the process, since electrode production is generally more expensive than a metal melt. In addition, production rates are relatively low compared to other atomization processes such as gas atomization and water atomization. 

This process, also termed rapid spinning cup (RSC) process, was invented in the early 1980 s contemporarily by Osaka University in Japan[191] and Battelle s Columbus Division in the US)192 Unlike water atomization where water streams or droplets are used to disintegrate a molten metal, a coherent fast-moving liquid layer is used in the RSC process. Liquid quenchants include water, oil, glycerine, and other commercial quenching liquids. The materials atomized with the spinning cup method include a wide variety of metals and alloys such as tin, lead, aluminum alloys, copper alloys, iron alloys (stainless steels and high speed tool steels), zinc alloys and superalloys.[192]... 

Droplet Formation in Water Atomization. In water atomization of melts, liquid metal stream may be shattered by impact of water droplets, rather than by shear mechanism. When water droplets at high velocities strike the liquid metal stream, some liquid metal fragments are knocked out by the exploding steam packets originated from the water droplets and subsequently contract into spheroidal droplets under the effect of surface tension if spheroidization time is less than solidification time. It is assumed that each water droplet may be able to knock out one or more metal droplet. However, the actual number of metal droplets produced by each water droplet may vary, depending on operation conditions, material properties, and atomizer designs. 

---